1. Field of the Invention
This invention relates to systems useful for flame spraying powdered materials primarily comprising thermoplastic polymeric resins, and more particularly, to a vent block that prevents surging when utilized in such systems.
2. Description of Related Art
Methods and apparatus useful for flame spraying powdered plastic resins onto substrates have previously been disclosed, for example, in U.S. Pat. Nos. 4,632,309; 4,934,595; and 5,282,753. In U.S. Pat. No. 5,282,753, a flame spray coating system is disclosed that utilizes an eductor disposed below a powder hopper for entraining plastic powder in a stream of conveying air. The entrained powder is carried by the conveying air through a flexible delivery hose to a flame spray gun which contacts the powder with a flame to soften the plastic before propelling it against the substrate being coated.
More recently, a flame spray gun has been developed that utilizes an eductor disposed inside the gun to draw the powdered plastic material through a flexible delivery hose from a supply canister to the gun. Such a flame spray gun is disclosed, for example, in U.S. Pat. No. 5,297,733. Difficulties were initially experienced in using this gun because of surging in the powder delivery rate that occurred even though the air flow rate through the eductor remained substantially constant.